1. Field of the Invention
This invention relates generally to hydrodynamic rotary seal assemblies that are suitable for environmental exclusion and lubricant retention, and for maintaining a film of lubricant at the dynamic sealing interface when the environment pressure is higher than the lubricant pressure. More particularly, the present invention provides a non-circular support surface which efficiently supports the non-circular flank of a hydrodynamic rotary sealing element against environmental pressure, thereby maintaining the functional integrity of the non-circular lubricant edge and the abrupt circular environment edge of the sealing element.
2. Background of the Invention
This invention relates to the commonly assigned prior art hydrodynamic rotary seals and sealing assemblies of U.S. Pat. Nos. 4,610,319, 5,195,754, 5,230,520, 5,678,829, 5,738,358, 5,823,541, 5,873,576, 6,120,036, 6,109,618, and 6,036,192 and PCT WO 95/03504. FIGS. 1-1C of this specification are cross-sectional views which represent prior art which is discussed herein to enhance the readers"" understanding of a problem associated with the prior art.
A typical example of such prior art hydrodynamic rotary seals is shown in the uninstalled condition in FIG. 1 generally at 2, and is shown in the intended installed condition in FIG. 1A in a rotary sealing assembly.
The hydrodynamic rotary seal consists of a resilient generally circular body 4, which incorporates a dynamic sealing surface 8, a hydrodynamic inlet curvature 7 and a non-circular flank 10. The dynamic sealing surface 8 has a has an abrupt circular environment exclusion edge 12, and also has a non-circular lubricant edge 14 established by the non-circular flank 10 and hydrodynamic inlet curvature 7.
Such hydrodynamic rotary seals are employed within a seal gland 16 of a housing 18, and are used to retain a lubricant 20 and to exclude an environment 22 which may contain contaminate matter. The dynamic sealing surface 8 establishes a sealing interface when compressed against a mating relatively rotatable surface 24, the footprint of said sealing interface having a footprint lubricant edge 28 and a footprint environment edge 30. The non-circular character of non-circular flank 10 causes the footprint of said sealing interface to be of varying width.
As relative rotation of relatively rotatable surface 24 takes place, the non-circular lubricant edge 14, which has a gradually converging relationship with the relatively rotatable surface 24 as a result of hydrodynamic inlet curvature 7 and non-circular flank 10, generates a hydrodynamic wedging action that forces a lubricant film between dynamic sealing surface 8 and relatively rotatable surface 24 per the teachings of U.S. Pat. No. 4,610,319. The lubricant is wedged into the dynamic sealing interface by the normal component Vn of the rotational velocity V acting on non-circular lubricant edge 14 of dynamic sealing surface 8. This lubricant film physically separates dynamic sealing surface 8 and relatively rotatable surface 24, and thereby prevents the typical frictional wear and heat damage associated with conventional non-hydrodynamic seals, and thereby prolongs seal life. Abrupt circular environment exclusion edge 12 does not generate a hydrodynamic wedging action with the environment in response to relative rotary motion because it is not skewed relative to rotational velocity V, and thereby functions to exclude environment 22 per the teachings of U.S. Pat. No. 4,610,319.
The prior art seals are best suited for applications in which the pressure of lubricant 20 is either higher than, or substantially balanced with, the pressure of environment 22. FIG. 1A shows the seal being held against environment-side gland wall 32 by pressure differential-induced hydrostatic force resulting from the lubricant 20 being at a higher pressure than environment 22. Owing to the complimentary shapes of the seal environmental end 34 and the environment-side gland wall 32, the seal is well supported by environment-side gland wall 32 in a manner that resists distortion and extrusion of body 4 when the pressure of lubricant 20 is higher than the pressure of environment 22.
As depicted in FIG. 1B, if the pressure of environment 22 is substantially higher than the pressure of lubricant 20, the resulting differential pressure-induced hydrostatic force can severely distort body 4, footprint lubricant edge 28 and a footprint environment edge 30. The hydrostatic force presses body 4 against lubricant-side gland wall 36, and can cause body 4 to twist and deform such that non-circular flank 10 and hydrodynamic inlet curvature 7 are substantially flattened against relatively rotatable surface 24. Such distortion and flatting can inhibit or eliminate the intended hydrodynamic lubrication, resulting in premature seal wear because footprint lubricant edge 28 can become substantially circular under such conditions, and the gently converging relationship between body 4 and relatively rotatable surface 24 (which is necessary for hydrodynamic lubrication) can be eliminated. Such distortion can also cause abrupt circular environment exclusion edge 12 to distort to a non-circular configuration and may also cause portions of dynamic sealing surface 8 to lift away from relatively rotatable surface 24, producing a low convergence angle 38 between dynamic sealing surface 8 and relatively rotatable surface 24, and causing the footprint environment edge 30 to become non-circular and skewed relative to rotational velocity V. Such distorted geometry is eminently suitable for the generation of a hydrodynamic wedging action in response to relative rotation of the relatively rotatable surface 24; such wedging action can force environmental contaminants into the sealing interface and cause rapid wear.
To effectively exclude a highly pressurized environment, one must use a pair of oppositely-facing prior art hydrodynamic seals; one to serve as a partition between the lubricant and the environment, and the other to retain the lubricant, which must be maintained at a pressure equal to or higher than the environment. This scheme ensures that neither seal is exposed to a high differential pressure acting from the wrong side, but requires a mechanism to maintain the lubricant pressure at or above the environment pressure. For example, see the first pressure stage of the drilling swivel of U.S. patent application Ser. No. 09/018,261.
Many applications, such as the oilfield drilling swivel, the progressing cavity artificial lift pump, centrifugal pumps, and rotary mining equipment would benefit significantly from a hydrodynamic rotary seal having the ability to operate under conditions where the environment pressure is higher than the lubricant pressure, because the resulting assembly would avoid the complexity and expense associated with lubricant pressurization.
The objective of the present invention is to provide a simple and compact rotary sealing assembly for lubricant retention and high pressure environmental exclusion which employs the advantage of maintaining a film of lubricant at the dynamic sealing interface during operation to thus promote efficiency and longevity of service.
A principle feature of the present invention is a seal gland wherein at least a portion of the lubricant-side gland wall is a non-circular support surface which supports the non-circular flank and hydrodynamic inlet curvature of a hydrodynamic rotary seal or packing against pressure-induced distortion when the environment pressure is higher than the lubricant pressure, so as to retain the hydrodynamic wedging function of the non-circular lubricant edge of the seal, and so as to retain the exclusionary function of the abrupt circular environment edge of the seal.
Another feature of the present invention is a seal gland wherein at least a portion of the non-circular support surface is angulated such that a component of hydrostatic force helps to support the angulated non-circular flank of a hydrodynamic rotary seal against pressure-induced distortion when the environment pressure is higher than the lubricant pressure.
Another feature of the present invention is the exploitation of the circularity of the environment-side gland wall to retain the circularity and the exclusionary function of the abrupt circular environment edge of a hydrodynamic rotary seal when the environment pressure is higher than the lubricant pressure.
Another feature of the present invention is the use of diagonal compression of a hydrodynamic rotary seal to retain the circularity and the exclusionary function of the abrupt circular environment edge of a hydrodynamic rotary seal when the environment pressure is higher than the lubricant pressure.
Another feature of the present invention is the compression of a portion of a hydrodynamic rotary seal between a first seal housing component and a second seal housing component to establish a seal between the first seal housing component and a second seal housing component and to prevent rotation of the seal within the seal gland.
Another feature of the present invention is the use of a flexible dynamic sealing rim, which may be fabric reinforced, to contain an environment pressure, which is higher than the lubricant pressure.
Another feature of the present invention is the use of a housing indexing element engaging a seal indexing geometry to align the non-circular features of a hydrodynamic seal with the non-circular features of a seal gland during installation of the seal into the gland.